Sirenidae, the sirens, are a family of aquatic salamanders. Family members have very small fore limbs, and lack hind limbs altogether. In one species, the skeleton in their fore limbs is made of only cartilage. In contrast to most other salamanders, they have external gills bunched together on the neck in both larval and adult states. Sirens are found only in the Southeastern United States and northern Mexico. They are the only herbivorous salamanders.